Vacuum pumps are used to create vacuum pressure for a variety of industrial applications. Most vacuum pump designs require internal lubrication; however, liquid ring vacuum pumps require no internal lubrication because there is no metal to metal contact between the rotating and stationary parts of the pump and the bearings are located external to the pumping chamber. The design of liquid ring vacuum pumps uses a multi-bladed impeller mounted on a shaft positioned eccentrically in a cylindrical pump housing. The pump housing is partially filled with a liquid sealant. Portplates with inlet and discharge openings are positioned on either side of the impeller. As the impeller rotates, the centrifugal force pushes the liquid sealant outward forming a liquid ring within the pump housing. The vacuum is created by the movement of the liquid outward inside the pump housing. The design of the liquid ring vacuum pump requires a continuous flow of fresh sealing liquid in the pump housing.
Liquid ring vacuum pumps typical use water as the sealing medium; however, the use of water has several drawbacks. In an open system, vacuum pumps can draw and discharge a continuous supply of fresh water from an external source. Environmental laws, restrictions on water usage, and the cost of water discharge disposal creates a need for a closed loop seal system, which recirculates the water. Recirculated water often picks up contaminants that can damage the pump. In addition, the water is heated in the operation of a liquid ring vacuum pump and must be cool before being recirculated back into the pump in a closed loop seal system. This necessitates the use of a heat exchanger in the seal system.
Waterless liquid ring vacuum pumps have been developed that use oil as the sealant. The use of oil as the sealant medium has several operational advantages over water, but it necessitates the use of a closed loop oil seal system. The operation of waterless liquid ring vacuum pumps, however, creates a significant oil separation problem for their oil seal systems. The rotation of the impeller inside the pump creates oil mist, which is a mixture of air and gaseous oil particulate. The oil mist is circulated through the closed loop oil seal system along with the oil discharge. Unlike oil mist, the water vapor created by the rotation of the impeller in a water based system can be simply vented into the atmosphere without significantly affecting the environment or the oil seal system. Consequently, oil seal systems for waterless liquid ring vacuum pumps must include air/oil separators, which separate the oil particulate contained in the oil mist from the air. The recaptured oil separated from the oil mist must be collected for recirculation, while the air is vented out of the system.
Heretofore, conventional air/oil separators have comprised simply a reservoir tank and a separate filter element. The reservoir tank collects the liquid oil from the oil discharge deposited into the separator from the vacuum pump, while the filter element collects the gaseous oil particulate from the oil mist in the oil discharge. Conventional filter elements use an oil absorbing composite fiberglass mesh, in which the oil particulate coalesces. This type of air/oil separator often fails to remove a significant portion of the oil particulate from the oil mist. The failure is often due to the velocity of the oil discharge through the separator, and the shear volume of oil discharge deposited into the separators. The oil mist often passes through the separator too quickly to permit sufficient condensation within the reservoir tank and too quickly to coalesce an acceptable portion of the oil particulate within the filter element. Consequently, the inefficiency of conventional air/oil separators represents a significant environmental and health hazard, as well as an operational problem.